Abstract
Calculations of the change of the reflectance of the beam splitter of a laser beam monitor resulting from small changes in direction of incidence, polarization, and divergence of the incident beam, are summarized. It is concluded that for angles of incidence less than about 30 degrees these changes in reflectance will not significantly change the responsivity of the monitor, whereas for a beam incident at 45 degrees considerable errors will result. The design and performance characteristics of a beam monitor in which a linearly polarized beam is incident on the beam splitter at 20 degrees are discussed.